R/download.mnist.R

In xrobin/mnist: MNIST dataset

# Load the MNIST digit recognition dataset into R
# http://yann.lecun.com/exdb/mnist/
# assume you have all 4 files and gunzip'd them
# creates train$n, train$x, train$y and test$n, test$x, test$y
# e.g. train$x is a 60000 x 784 matrix, each row is one digit (28x28)
# call: show_digit(train$x[5,]) to see a digit.
# brendan o'connor - gist.github.com/39760 - anyall.org

load_image_file <- function(conn) {
	readBin(conn, 'integer', n=1, size=4, endian='big')
	n = readBin(conn, 'integer', n=1, size=4, endian='big')
	nrow = readBin(conn, 'integer', n=1, size=4, endian='big')
	ncol = readBin(conn, 'integer', n=1, size=4, endian='big')
	x = readBin(conn, 'integer', n=n*nrow*ncol, size=1, signed=F)
	x = matrix(x,  ncol=nrow * ncol,  byrow=T)
	close(conn)
	return(x)
}

load_label_file <- function(conn) {
	readBin(conn, 'integer', n=1, size=4, endian='big')
	n = readBin(conn, 'integer', n=1, size=4, endian='big')
	y = readBin(conn, 'integer', n = n, size=1, signed=F)
	close(conn)
	return(y)
}

download.mnist <- function(range = c(0, 1), global = FALSE) {
	mnist <- list(
		train = list(),
		test = list()
	)
	
	mnist$train$x <- load_image_file(gzcon(url("http://yann.lecun.com/exdb/mnist/train-images-idx3-ubyte.gz", "rb")))
	mnist$test$x <- load_image_file(gzcon(url("http://yann.lecun.com/exdb/mnist/t10k-images-idx3-ubyte.gz", "rb")))
	mnist$train$y <- load_label_file(gzcon(url("http://yann.lecun.com/exdb/mnist/train-labels-idx1-ubyte.gz", "rb")))
	mnist$test$y <- load_label_file(gzcon(url("http://yann.lecun.com/exdb/mnist/t10k-labels-idx1-ubyte.gz", "rb")))
	
	# Normalize the x's - only if needed
	if (!isTRUE(all.equal(c(0, 255), range))) {
		if (! is.numeric(range))
			stop("'range' must be a numeric vector")
		if (length(range) != 2)
			range <- range(range)
		
		mnist$train$x <-  mnist$train$x / (255 / diff(range)) + range[1]
		mnist$test$x <-  mnist$test$x / (255 / diff(range)) + range[1]
		
		# Convert to integer if possible
		s <- seq(range[1], range[2], length.out = 256)
		if (isTRUE(all.equal(s, as.integer(s)))) {
			storage.mode(mnist$train$x) <- "integer"
			storage.mode(mnist$test$x) <- "integer"
		}
	}
	
	if (global) {
		save(mnist, file = paste(system.file(package="mnist"), "data", "mnist.RData", sep=.Platform$file.sep))
		assign("mnist", mnist, envir = globalenv())
	}
	
	return(mnist)
}